Mongodb：如何將 $lookup 和 map 的結果分組到包含匹配鍵的列表對象中？

Question

我有包含“模塊”的課堂文檔，整個文檔如下所示：

{
    "_id": "628a7ea21e2a666d7872efbf",
    "name": "Test Class",
    "owner": "60763491b98b9e186ef33137",
    "schoolId": "607dff27c712219af1e65d83",
    "description": "This is a test class.",
    "roster": [],
    "modules": [
        {
            "name": "Test Module 1",
            "id": "62a7082d0bf84c43fdfe95ff",
            "isPublished": false
        },
        {
            "name": "Test Module 2",
            "id": "62a72d6378ce044dca32e1a2",
            "isPublished": false
        }
    ]
}

我也有這樣的任務文件：

{
    "classroomId": "628a7ea21e2a666d7872efbf",
    "moduleId": "62a7082d0bf84c43fdfe95ff",
    "name": "Assignment 1",
    "description": "Test description",
    "created": 1655120822055,
    "reading": null,
    "questions": [],
    "isPublished": true,
    "_id": "62a723b6683ffc4b11940c7b"
}

我的問題是如何進行聚合，以便如果我想查找課堂作業，我可以按 moduleId 對作業文檔進行分組，然后將它們作為一個字段添加到模塊數組中。 最終文件是這樣的：

{
    "_id": "628a7ea21e2a666d7872efbf",
    "name": "Test Class",
    "owner": "60763491b98b9e186ef33137",
    "schoolId": "607dff27c712219af1e65d83",
    "description": "This is a test class.",
    "roster": [],
    "modules": [
        {
            "name": "Test Module 1",
            "id": "62a7082d0bf84c43fdfe95ff",
            "isPublished": false,
            "assignments": [
                {
                    "_id": "62a708ab0bf84c43fdfe9600",
                    "classroomId": "628a7ea21e2a666d7872efbf",
                    "moduleId": "62a7082d0bf84c43fdfe95ff",
                    "name": "Assignment 1",
                    "description": "Test description",
                    "created": 1655113899629,
                    "due": null,
                    "settings": null,
                    "reading": null,
                    "questions": [],
                    "isPublished": true
                },
                {
                    "_id": "62a723b6683ffc4b11940c7b",
                    "classroomId": "628a7ea21e2a666d7872efbf",
                    "moduleId": "62a7082d0bf84c43fdfe95ff",
                    "name": "Assignment 1",
                    "description": "Test description",
                    "created": 1655120822055,
                    "due": null,
                    "settings": null,
                    "reading": null,
                    "questions": [],
                    "isPublished": true
                }
            ]

        },
        {
            "name": "Test Module 2",
            "id": "62a72d6378ce044dca32e1a2",
            "isPublished": false,
            "assignments": [

            ]
        }
    ]
}

現在我只有基本查找，顯然這只是讓我得到一個單獨的分配字段，沒有組。

lookup = [
    {
        $lookup: {
            from: "assignments",
            localField: "modules.id",
            foreignField: "moduleId",
            as: "assignments"
        }
    }
];

Answer 1

1. $lookup

2. $set - 設置modules字段。

   2.1. $map - 迭代modules數組並返回一個新數組。

   2.1.1. $mergeObject - 將當前迭代module文檔與結果2.1.1.1中帶有assignments數組的文檔合並。

   2.1.1.1。 $filter - 通過匹配moduleId過濾assignments數組。

3. $unset - 刪除assignments字段。

db.classroom.aggregate([
  {
    $lookup: {
      from: "assignments",
      localField: "modules.id",
      foreignField: "moduleId",
      as: "assignments"
    }
  },
  {
    $set: {
      modules: {
        $map: {
          input: "$modules",
          as: "module",
          in: {
            $mergeObjects: [
              "$$module",
              {
                "assignments": {
                  $filter: {
                    input: "$assignments",
                    as: "asgn",
                    cond: {
                      $eq: [
                        "$$module.id",
                        "$$asgn.moduleId"
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  },
  {
    $unset: "assignments"
  }
])

示例 Mongo 游樂場